The instant invention relates to the recovery of oil from oil spills on the surfaces of bodies of water and more particularly to a method and apparatus for recovering oils, such as those containing high viscosity residual oil fractions, from the surfaces of bodies of water.
The assignee's U.S. Pat. No. 5,023,002 to Schweizer et al, which issued in June of 1991, disclosed one of the first effective methods and apparatus for recovering oil from oil spills on the surfaces of bodies of water. Specifically, the Schweizer et al patent disclosed a method and apparatus in which an oil-water mixture can be quickly and effectively separated into essentially pure oil and pure water outlet streams utilizing a multi-stage coalescer unit. More specifically, the aforementioned Schweizer et al patent disclosed the concept of adding an oil-based solvent to an oil-water mixture recovered from the surface of a body of water in order to reduce the viscosity of the oil in the oil-water mixture to a level which permits the oil-water mixture to be effectively separated in an oil-water coalescer without causing the coalescer to become fouled or clogged. However, despite the fact that the method and apparatus disclosed in the aforementioned Schweizer et al U.S. patent have been found to be extremely effective for separating the oil in an oil-water mixture recovered from an oil spill from the water recovered therewith, it has been found that in some instances, particularly when dealing with crude oils having extremely high viscosity residual oil fractions, it can be impractical to add sufficient quantities of solvent to make it possible to process an oil-water mixture in an oil-water coalescer. For example, it has been found that in some instances it is impractical to carry sufficient quantities of solvent on board a marine vessel operating on the surface of a body of water in order to process an oil-water mixture containing a high viscosity residual oil fraction in a continuous on-board operation wherein separated water is returned to the body of water.
The instant invention represents a significant improvement over the previously known methods and apparatus by providing an effective method and apparatus which is operative for separating an oil-water mixture recovered from the surface of a body of water into essentially pure oil and pure water streams without the use of excessive quantities of solvent. Specifically, the instant invention provides an effective method and apparatus wherein an oil-water mixture recovered from the surface of a body of water is pre-treated in a first stage oil-water coalescer containing an interceptor having an extremely low surface area ratio so as to enable it to be utilized as a first stage processing unit for processing an oil-water mixture without first adding a solvent to reduce the viscosity of the oil therein.
Accordingly, the apparatus of the instant invention comprises means for continuously withdrawing a feed oil-water mixture from the surface of a body of water, and a first stage coalescer section for receiving the feed oil-water mixture and for separating it into a first oil outlet stream and a first reduced oil-water mixture stream. The first stage coalescer section comprises an interceptor having a surface area ratio between approximately 27 square feet per cubic foot and 65 square feet per cubic foot. The first stage oil-water coalescer section preferably comprises a corrugated plate vane-type coalescer comprising a plurality of spaced corrugated vanes. In this regard, it has been found that a first stage coalescer section of this type is capable of effectively processing oil-water mixtures containing oils having extremely high viscosity residual oil fractions without becoming fouled or plugged. It has been further found that a first stage coalescer section of this type is capable of separating out a large percentage of the oil in an oil-water mixture so that the first reduced oil-water mixture stream only contains a relatively small quantity of oil. The apparatus of the subject invention further comprises means for adjusting the viscosity of the oil in the first reduced oil-water mixture, preferably by adding a solvent thereto, and a second stage coalescer section for processing the first reduced oil-water mixture. The second stage coalescer section preferably comprises an interceptor, such as a wire mesh, having a surface area ratio between approximately 65 square feet per cubic foot and 2500 square feet per cubic foot, so that it is capable of effectively separating the first reduced oil-water mixture stream into a second oil outlet stream and a second reduced oil-water mixture stream which only contains a very small quantity of oil. The apparatus preferably still further comprises a third stage oil-water coalescer section and means for adjusting the viscosity of the oil in the second reduced oil-water mixture stream to a level below approximately 80 centipoise so that the second reduced oil-water mixture stream can be effectively processed in the third stage oil-water coalescer section without causing the third stage oil-water coalescer section to become clogged or fouled. The third stage oil-water coalescer section preferably comprises an interceptor having a surface area ratio between approximately 500 square feet per cubic foot and 4200 square feet per cubic foot, and it is operative for separating the second reduced oil-water mixture stream into substantially pure oil and pure water outlet streams.
Accordingly, the method of the subject invention is carried out by continuously withdrawing a feed oil-water mixture from the surface of a body of water, continuously passing the feed oil-water mixture through the first stage oil-water coalescer section to separate the feed oil-water mixture into a first oil outlet stream and a first reduced oil-water mixture stream, and adjusting the viscosity of the oil in the first reduced oil-water mixture stream to a level below approximately 80 centipoise. The viscosity adjusted first oil-water mixture stream is then passed through a second stage oil-water coalescer section to separate the viscosity adjusted first reduced oil-water mixture stream into a second oil outlet stream and a second reduced oil-water mixture stream, and the oil in the second reduced oil-water mixture stream is adjusted to a viscosity level of below approximately 80 centipoise. The viscosity adjusted second reduced oil-water mixture stream is then passed through the third stage oil-water coalescer section in order to separate the viscosity adjusted second reduced oil-water mixture stream into a third oil outlet stream and a water outlet stream. The viscosity of the oil in the first reduced oil-water mixture stream, and the viscosity of the oil in the second reduced oil-water mixture stream are preferably adjusted by adding a hydrophobic hydrocarbon oil solvent thereto. The first stage oil-water coalescer section preferably has a surface area ratio between approximately 27 square feet per cubic foot and 65 square feet per cubic foot; the second stage oil-water coalescer section preferably has a surface area ratio between approximately 65 square feet per cubic foot and 2500 square feet per cubic foot; and the third stage oil-water coalescer section preferably has a surface area ratio between approximately 500 square feet per cubic foot and 4200 square feet per cubic foot. The first stage oil-water coalescer section preferably comprises a corrugated plate vane-type coalescer which is designed so that it is operative for separating a high viscosity oil from water without clogging or fouling.
It has been found that the method and apparatus of the instant invention can be effectively utilized for separating oil recovered from the surface of a body of water from water recovered with the oil. Specifically, it has been found that the first stage oil-water coalescer section is capable of effectively separating most of the oil recovered from the surface of a body of water from the water recovered therewith without fouling or clogging. Further, it has been found that by adding a solvent to the first reduced oil-water mixture stream from the first stage oil-water coalescer section it is possible to reduce the viscosity of the oil therein to a level which enables the first reduced oil-water mixture stream to be processed in the second and third stage coalescer sections. Still further, it has been found that by adding further solvent to the second reduced oil-water mixture stream from the second stage oil-water coalescer section in order to assure that the viscosity of the oil in the second reduced oil-water mixture is below approximately 80 centipoise, it is possible to effectively process the second reduced oil-water mixture stream so as to produce essentially pure oil and water streams from the third stage oil-water coalescer section. Still further, it has been found that because the solvent is only added to the first and second reduced oil-water mixture streams, rather than to the feed inlet stream, the process can be carried out with a minimal amount of solvent. As a result, the apparatus of the subject invention can be effectively utilized on board a vessel navigating on a body of water for cleaning up an oil spill on the surface of body of water.
Accordingly, it is a primary object of the instant invention to provide an improved apparatus for recovering a hydrophobic, hydrocarbon oil from the surface of a body of water.
Another object of the instant invention is to provide an effective method of recovering a hydrophobic, hydrocarbon oil from the surface of a body of water.
An even still further object of the instant invention is to provide an effective oil-water coalescer apparatus for recovering a hydrophobic, hydrocarbon oil from the surface of a body of water utilizing a minimal amount of hydrocarbon solvent.
An even still further object of the instant invention is to provide an effective apparatus which can be practically mounted and operated on a vessel navigating on a body of water for separating an oil-water mixture recovered from an oil spill on the body of water.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing.